There are number of UPSs known in the prior art which use half-bridge inverters and a single battery source. U.S. Pat. No. 4,935,861, which issued in the name of Johnson et al., describes one example of such a device. In the Johnson UPS, both capacitors C1 and C2 of the half-wave inverter are charged to the same voltage from a single battery source. Johnson uses a DC-DC converter to charge both capacitors. The charging current is the same for either capacitor. This condition creates a problem when the inverter load is not symmetrical because the load current values and waveforms then differ for positive and negative periods of an alternating voltage. In half-bridge inverter, one capacitor supplies energy during the positive portion of the output AC voltage and the other capacitor supplies energy during the negative portion. Thus, both capacitors will be discharged unequally by the non-symmetrical load but will be charged equally by identical current flow from a charger. This condition will lead to a total discharge of one capacitor which will render the inverter inoperable for its intended purpose due to its inability to produce a symmetrical AC voltage waveform.